Epitaxial Synthesis of Highly Oriented 2D Janus Rashba Semiconductor BiTeCl and BiTeBr Layers

Abstract

The family of layered BiTeX (X = Cl, Br, I) compounds are intrinsic Janus semiconductors with giant Rashba-splitting and many exotic surface and bulk physical properties. To date, studies on these materials required mechanical exfoliation from bulk crystals which yielded thick sheets in nonscalable sizes. Here, we report epitaxial synthesis of Janus BiTeCl and BiTeBr sheets through a nanoconversion technique that can produce few triple layers of Rashba semiconductors (<10 nm) on sapphire substrates. The process starts with van der Waals epitaxy of Bi2Te3 sheets on sapphire and converts these sheets to BiTeCl or BiTeBr layers at high temperatures in the presence of chemically reactive BiCl3/BiBr3 inorganic vapor. Systematic Raman, XRD, SEM, EDX, and other studies show that highly crystalline BiTeCl and BiTeBr sheets can be produced on demand. Atomic level growth mechanism is also proposed and discussed to offer further insights into growth process steps. Overall, this work marks the direct deposition of 2D Janus Rashba materials and offers pathways to synthesize other Janus compounds belonging to MXY family members.

Reaching the Excitonic Limit in 2D Janus Monolayers by In Situ Deterministic Growth

“…Subsequently, the top surface is converted to sulfur using the selective epitaxial atomic replacement (SEAR) method to yield the monolayer Janus TMD counterpart. [ 9 ] Here, the pressure within the chamber is tuned to a few hundred mTorr, such that the mean free path of the radicals is sufficiently high to favor etching of only the top chalcogen layer. Furthermore, the energy of the hydrogen and sulfur radicals is carefully tuned by modulating the power of the RF generator above the energy of the transition metal–selenium bond to remove Se atoms, but below the energy of the transition metal–sulfur bond to keep the sulfur surface intact ( Table 1 ) after selenium vacancies (V Se ) are modified with reactive sulfur radicals (Figure 1c).…”

“…Recognizing these opportunities and challenges, previous work from our team and others has employed high-temperature processing, epitaxial conversion, and pulsed laser deposition to transform 2D classical layers into Janus structures. [4,5,[9][10][11][12] These growth methods are at their primal stages and produce low-quality monolayers; first, these techniques require intense growth conditions, and thus Janus monolayers are at the cusp of alloying or heavily defected with poor electronic/optical quality. [4,5,9,10] Thus, the photoluminescence (PL) of SMoSe and SWSe Janus monolayers exhibits a large bound exciton peak related to defects or a rather broad PL peak due to strain, alloying, and defects.…”

“…[4,5,[9][10][11][12] These growth methods are at their primal stages and produce low-quality monolayers; first, these techniques require intense growth conditions, and thus Janus monolayers are at the cusp of alloying or heavily defected with poor electronic/optical quality. [4,5,9,10] Thus, the photoluminescence (PL) of SMoSe and SWSe Janus monolayers exhibits a large bound exciton peak related to defects or a rather broad PL peak due to strain, alloying, and defects. Second, these techniques lack in situ growth monitoring tools and, therefore, Janus monolayers Named after the two-faced Roman god of transitions, transition metal dichalcogenide (TMD) Janus monolayers have two different chalcogen surfaces, inherently breaking the out-of-plane mirror symmetry.…”

First-principles study on structural, vibrational, elastic, piezoelectric, and electronic properties of the Janus BiXY ( X=S,Se,T

“…Additionally, bulk crystals of BiSI and BiSeI, which are stable at high temperatures, have been synthesized in large quantities by a ball milling method and have been shown to exhibit suitable optical band gaps for solar cell applications [40]. Lately, highly crystalline 2D BiTeCl and BiTeBr nanosheets, which can be utilized in spintronics [41], have been directly synthesized via epitaxial growth [42].…”

Tuning MoSO monolayer properties for optoelectronic and spintronic applications: effect of external strain, vacancies and doping

“…Results indicate prospect of their electronic, optical, and piezoelectric properties. [24][25][26][27] Semiconductor layered BiTeCl and BiTelBr compounds with giant Rashba-splitting have been prepared by Debarati et al 28 Theoretical calculations yield small energy gaps of 0.83 and 0.80 eV, 29 respectively. Besides, a large variety of Janus single layers based on chalcogens and halogens with feature-rich properties have been reported in the computational 2D materials database (C2DB).…”